A known magnetic drive pump described in JP2005-139917A discloses a water pump which includes an impeller rotatably supported in a pump chamber so as to generate a flow of the fluid in the pump chamber by the rotation thereof and a drive mechanism which rotates the impeller. The drive mechanism includes a permanent magnet integrally fixed to a drive magnet rotatably positioned outside relative to a partition wall which separates the pump chamber from the outside, and an inductor including a conductor which is rotated by the induced current generated by the rotation of the permanent magnet. With the construction of the water pump (i.e., the magnetic drive pump) described in JP2005-139917A, because a flow rate of the coolant (i.e., workload of the pump) increases nonlinearly in response to an increase of an engine rotation speed, the workload of the pump during high engine rotation speed can be appropriately set compared to the conventional water pump in which a flow rate of the coolant increases linearly. However, according to the construction of the water pump described in JP2005-139917A, in a middle engine rotation range, during cold start and warm up, or in an engine operation range in which not much circulation of the coolant is required such as when a vehicle travels in constant speed with small engine output, undue volume of the coolant is circulated, which is a cause of a decline of an engine warm-up performance and a decline of fuel economy because of unnecessary workload.
A need thus exists for a magnetic drive pump, which is capable of shortening a rise time of coolant temperature by declining a flow rate of coolant during cold start and warm up of, an engine and of improving fuel economy by reducing the workload of a pump by reducing the flow rate of coolant.